astronomy

Small Astronomy Satellite 3

Small Astronomy Satellite 3 is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Small Astronomy Satellite 3 rather than just read about it. In short: The Small Astronomy Satellite 3 (SAS 3, also known as SAS-C before launch) (Explorer 53) was a NASA X-ray astronomy space telescope. It functioned from 7 May 1975 to 9 April 1979.

Key takeaways

Small Astronomy Satellite 3 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Small Astronomy Satellite 3 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Small Astronomy Satellite 3 from memory before moving on to harder problems.

Reference excerpt

The Small Astronomy Satellite 3 (SAS 3, also known as SAS-C before launch) (Explorer 53) was a NASA X-ray astronomy space telescope. It functioned from 7 May 1975 to 9 April 1979. It covered the X-ray range with four experiments on board. The satellite, built by the Johns Hopkins University Applied Physics Laboratory (APL), was proposed and operated by MIT's Center for Space Research (CSR). It was launched on a Scout vehicle from the Italian San Marco platform (Broglio Space Center) near Malindi, Kenya, into a low-Earth, nearly equatorial orbit. It was also known as Explorer 53, as part of NASA's Explorer program. The spacecraft was 3-axis stabilized with a momentum wheel that was used to establish stability about the nominal rotation, or Z-axis. The orientation of the Z-axis could be altered over a period of hours using magnetic torque coils that interacted with the Earth's magnetic field. Solar panels charged batteries during the daylight portion of each orbit so that SAS 3 had essentially no expendables to limit its lifetime beyond the life of the tape recorders, batteries, and orbital drag. The spacecraft typically operated in a rotating mode, spinning at one revolution per 95-minute orbit, so that the LEDs, tube and slat collimator experiments, which looked out along the Y-axis, could view and scan the sky almost continuously. The rotation could also be stopped, allowing extended (up to 30 minutes) pointed observations of selected sources by the Y-axis instruments. Data were recorded on board by magnetic tape recorders, and played back during station passes every orbit. SAS 3 was commanded from the NASA Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, but data was transmitted by modem to MIT for scientific analysis, where scientific and technical staff were on duty 24 hours a day. The data from each orbit were subjected to quick-look scientific analysis at MIT before the next orbital station passed, so the science operational plan could be altered by telephoned instruction from MIT to GSFC in order to study targets in near real-time.

Launch The spacecraft was launched from the San Marco platform off the coast of Kenya, Africa, into a near-circular, near-equatorial orbit. This spacecraft contained four instruments: the Extragalactic Experiment, the Galactic Monitor Experiment, the Scorpio Monitor Experiment and the Galactic Absorption Experiment. In the orbital configuration, the spacecraft was 145.2 cm (57.2 in) high and the tip-to-tip dimension was 470.3 cm (185.2 in). Four solar paddles were used in conjunction with a 12-cell nickel–cadmium battery to provide power over the entire orbit. The spacecraft was stabilized along the Z-axis and rotated at about 0.1°/seconds. Changes to the spin-axis orientation were by ground command, either delayed or in real-time. The spacecraft could be made to move back and forth ± 2.5° across a selected source along the X-axis at 0.01°/seconds. The experiments looked along the Z-axis of the spacecraft, perpendicular to it, and at an angle.

Objectives The major scientific objectives of the mission were:

Determine bright X-ray source locations to an accuracy of 15 arcseconds; Study selected sources over the energy range 0.1-55 keV; Continuously search the sky for X-ray novae, flares, and other transient phenomena. Explorer 53 (SAS-C) was a small spacecraft whose objectives were to survey the celestial sphere for sources radiating in the X-ray, gamma ray, ultraviolet and other spectral regions. The primary missions of Explorer 53 were to measure the X-ray emission of discrete extragalactic sources, to monitor the intensity and spectra of galactic X-ray sources from 0.2 to 60-keV, and to monitor the X-ray intensity of Scorpio X-1.

Experiments

Extragalactic Experiment (EGE) This experiment determined the positions of very weak extragalactic X-ray sources. The instrument viewed a 100-sq-degree region of the sky around the direction of the spin axis of the satellite. The nominal targets for a 1-year study were: (1) the Virgo Cluster of galaxies for 4 months, (2) the galactic equator for 2 months, (3) the Andromeda Nebula for 3 months, and (4) the Magellanic Clouds for 3 months. The instrumentation consisted of one 2.5-arc-minutes and one 4.5-arc-minutes Full width at half maximum (FWHM) modulation collimator, as well as proportional counters sensitive over the energy range from 1.5 to 10-keV. The effective area of each collimator was about 225 cm2. The aspect system provided information on the orientation of the collimators to an accuracy of 15-arc-seconds.

Galactic Absorption Experiment (GAE) The density and distribution of interstellar matter were determined by measuring the variation in the intensity of the low-energy diffuse X-ray background as a function of galactic latitude. A 1-micrometer polypropylene window proportional counter was used for the 0.1- to 0.4-keV and 0.4- to 1.0-keV energy ranges, while a 2-micrometer titanium window counter covered the energy range from 0.3 to 0.5 keV. In addition, two 1-mm beryllium window counters were used for the 1.0- to 10-keV energy range. The collimators in this experiment had fields of view of 3° for the 1-micrometer counter, 2° for the 2-mm counter, and 2° for the 1-mm counters.

Galactic Monitor Experiment (GME) The objectives of this experiment were to locate galactic X-ray sources to 15 arc-seconds and to monitor these sources for intensity variations. The source positions were determined with the use of the modulation collimators of the Extragalactic Experiment during the nominal 2-month observation of the galactic equator. The monitoring of the X-ray sky was accomplished by the use of three slat collimators. One collimator, 1° by 70° FWHM, was oriented perpendicular to the equatorial plane of the satellite, while the other two, each 0.5° by 45° FWHM, were oriented 30° above and 30° below the first. The detector behind each collimator was a proportional counter, sensitive from 1.5 to 13 keV, with an effective area of about 100 cm2. The 1.0° collimator had an additional counter of the same area, sensitive from 8 to 50 keV. Three lines of position were obtained for any given source when the satellite was being spun at a steady rotation of 4 arc-minutes/seconds about the Z-axis.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Small Astronomy Satellite 3

Start with the simplest possible case. Write down what Small Astronomy Satellite 3 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Small Astronomy Satellite 3 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Small Astronomy Satellite 3 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Small Astronomy Satellite 3

In research: Small Astronomy Satellite 3 appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Small Astronomy Satellite 3 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Small Astronomy Satellite 3 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1975 in spaceflight, Explorers Program, Satellites formerly orbiting Earth, so understanding it makes those chapters shorter.
In everyday life: Look for Small Astronomy Satellite 3 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Small Astronomy Satellite 3 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Small Astronomy Satellite 3 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Small Astronomy Satellite 3 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Small Astronomy Satellite 3 in simple terms?

The Small Astronomy Satellite 3 (SAS 3, also known as SAS-C before launch) (Explorer 53) was a NASA X-ray astronomy space telescope. It functioned from 7 May 1975 to 9 April 1979.

Why does Small Astronomy Satellite 3 matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Small Astronomy Satellite 3?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Small Astronomy Satellite 3.